Function of the fibres and interfibre bonds strength during accelerated ageing of paper

Assuming that the dimensional parameters (L-1, D) and structure (RBA) of pa per do not undergo any changes, a decrease in the strength of paper observe d during accelerated ageing can result, according to equation l, from a dec rease of the strength of fibres (l(t0)), interfibre bonds, or from both of them. In this work, both parameters will be investigated during accelerated agein g of standard laboratory sheets and standard duplex sheets, namely neutral slightly and strongly acidified by aluminium sulphate. The results obtained have shown that the neutral sheets retain the strength of fibres, interfibre bonds and sheets. On the contrary, the slightly acid ified and acid sheets manifest a decreased strength of fibres, while the st rength of interfibre bonds measured as cohesion in shearing (sigma(s)), pee ling of (sigma(p)) and z-direction (sigma(z)) remains unchanged. From the m easured values, there follows that a drop in the strength of sheets during accelerated ageing is caused by the strength of fibres.